1. Field of the Invention
Embodiments of the present invention generally relate to ultra wide band (UWB) communication systems. More particularly, embodiments of the present invention generally relate to apparatuses and methods generating radio frequency (RF) signals used in a multi-band of a UWB communication system.
2. Description of the Related Art
In general, communication systems use frequencies within a predetermined band to transmit and receive data. The data used in the communication systems can be classified into circuit data and packet data. The circuit data must be transmitted and received in real time, such as voice signals. The packet data has a predetermined bandwidth, or a greater bandwidth, and is not necessarily transmitted in real time, unlike the circuit data. The frequency band used to transmit the circuit data is generally narrow while the frequency band used to transmit the packet data may be wider.
As described above, when the amount of data to be transmitted increases, an increased frequency band may be used. Hereinafter, the wider frequency band can be referred to as an ultra wide band (UWB). The UWB can be divided into a plurality of sub-bands, each having a predetermined bandwidth. A UWB communication system can transmit data using the plurality of sub-bands to transmit and receive a large amount of data per unit time. The UWB communication system selects one of the plurality of sub-bands and transmits data using the selected sub-band so as to increase security for data. In other words, the UWB communication system sequentially uses the plurality of sub-bands so as to increase the security for the transmitted data.
FIG. 1 illustrates frequency band(s) used in a conventional UWB communication system. As shown in FIG. 1, the frequency band used in the UWB communication system can be 3432 MHz to 10032 Mhz, for example. In this example, the frequency band can be divided into four sub-band groups A, B, C and D. The group A may include three sub-bands, group B may include two sub-bands, group C may include four sub-bands, and group D may include four sub-bands
In this example, reference frequencies of the three sub-bands of the group A can be 3432 MHz, 3960 MHz, and 4488 MHz, respectively, the reference frequencies of the two sub-bands of the group B can be 5016 MHz and 5808 Mhz, respectively, reference frequencies of the four sub-bands of the group C can be 6336 MHz, 6864 MHz, 7392 MHz, and 7920 MHz, respectively, and the reference frequencies of the four sub-bands of the group D can be 8448 MHz, 8976 MHz, 9504 MHz, and 10032 Mhz, respectively. The two sub-bands of the group B may overlap with frequency bands used in a currently used wireless local area network (WLAN), and in this example, the four sub-bands of the group D may not be currently used in the current level of technology.
As described above, a UWB communication system necessarily requires an appropriate structure to generate signals having reference frequencies used therein. Hereinafter, the structure of such a UWB communication system will be described, along with the corresponding method of generating the signals having the reference frequencies used in such a UWB communication system.
FIG. 2 illustrates the structure of a receiver in a UWB communication system. The corresponding structure of a transmitter of such a UWB communication system can be derived based on the same.
The receiver of the UWB communication system includes an antenna 200, a band pass filter (BPF) 202, a mixing stage including mixers 204 and 206, low pass filters (LPFs) 208 and 210, variable gain amplifiers (VGAs) 212 and 214, analog-to-digital converters (ADCs) 216 and 218, and a sub-band generator (SBG) 220. In addition to these components, the UWB communication system may include additional and/or alternate components.
The antenna 200 transmits a wireless signal to and/or receives a wireless signal from the transmitter of the UWB communication system. The BPF 202 extracts only a signal having a frequency used in the UWB communication system from the wireless signal. The frequency used in the UWB communication system is generally 3 GHz to 5 GHz. The signal having passed through the BPF 202 is transmitted to the mixers 204 and 206. The mixer 204 receives a signal generated by the SBG 220. The SBG 220 will be described in detail later with reference to FIGS. 3 and 4. The SBG 220 generates both a signal that is not phase shifted and a signal that is 90° phase shifted and transmits the signal that is not phase shifted to the mixer 204 and the signal that is 90° phase shifted to the mixer 206.
The mixer 204 mixes the received signals and transmits the mixed signal to the LPF 208. The LPF 208 removes a noise component from a low frequency of the mixed signal generated in the mixing process. The LPF 208 extracts only one of a plurality of reference frequencies (which have been converted into low frequency signals through the mixing process) used in the UWB communication system. The VGA 212 corrects a magnitude of a received signal to be more constant. The ADC 216 converts a received analog signal into a digital signal. The operations of the mixer 206, the LPF 210, the VGA 214, and the ADC 218 can be the same as those of the mixer 204, the LPF 208, the VGA 212, and the ADC 216 and thus will not be described herein.
FIG. 3 illustrates the structure of the SBG 220 shown in FIG. 2. The SBG 220 includes a local oscillator 300, a phase-locked loop (PLL) 302, divide by 8 and divide by 2 dividers 304 and 306, single side bands (SSBs) 308 and 312, and a selector 310. The SBG 220 generating the three reference frequencies of the illustrated group A will now be described with reference to FIG. 3.
The local oscillator 300 generates a signal having a frequency of 4224 MHz. The PLL 302 stabilizes the frequency of the signal generated by the local oscillator 300. The signal generated by the local oscillator 300 is then transmitted to the divide by 8 divider 304 and the SSB 312. The divide by 8 divider 304 divides the frequency of the signal by 8. A frequency of a signal output from the divide by 8 divider 304 is 528 MHz. The signal divided by the divide by 8 divider 304 is transmitted to the divide by 2 divider 306 and the SSB 308. The divide by 2 divider 306 divides a frequency of the received signal by 2. Thus, a frequency of a signal output from the divide by 2 divider 306 is 264 MHz. The signal divided by the divide by 2 divider 306 is then transmitted to the SSB 308 and the selector 310. The SSB 308 mixes the signal having the frequency of 528 MHz and the signal having the frequency of 264 MHz to generate a signal having a frequency of 792 MHz. The signal generated by the SSB 308 is transmitted to the selector 310. The selector 310 selects one of the signals having the frequencies of 264 MHz or 792 MHz and transmits the selected signal to the SSB 312.
The SSB 312 mixes and outputs the signal having the frequency of 4224 MHz transmitted from the local oscillator 300 and one of the signals having the frequencies 264 MHz and 792 MHz selected by the selector 310. In more detail, when the SSB 312 receives the signal having the frequency of 264 MHz from the selector 310, the SSB 312 generates and outputs signals having frequencies of 3960 MHz and 4488 MHz. When the SSB 312 receives the signal having the frequency of 792 MHz from the selector 310, the SSB 312 generates and outputs a signal having a frequency of 3432 MHz. The SGB 220 thus selects and generates one of the signals having the frequencies of 3960 MHz, 4488 MHz, and 3432 Mhz, for example, using the above-described structures.
FIG. 4 illustrates another example of an SBG. Elements in FIG. 4 similar to those of FIG. 3 will not be further described herein. Rather, hereinafter, the structure of the SBG will be described based on phase shifters 410 and 420 and SSBs 308 and 312. The phase shifters 410 and 420 generate and output signals that are phase shifted and signals that are not phase shifted. In general, the two signals output from the phase shifter 410 or 420 have a phase difference of 90°.
The operation of the SSB 308 will now be described. Here, the Q component of an intermediate frequency (IF) signal (transmitted to the phase shifter 410) is input to a mixer 412 and an I component of the IF signal is input to a mixer 414. The Q component of the IF signal input to the mixer 412 is sin(w IFt), and the I component of the IF signal input to the mixer 414 is cos(w IFt). An I component of a local oscillator (LO) signal (transmitted from the phase shifter 408) is input to the mixer 412, and a Q component of the LO signal is input to the mixer 414. The operations of the mixers 412 and 414 are set forth using Equations 1 and 2 below, respectively:
                                          sin            ⁡                          (                                                w                  LO                                ⁢                t                            )                                ⁢                      cos            ⁡                          (                                                w                  IF                                ⁢                t                            )                                      =                              1            2                    ⁡                      [                                          sin                ⁡                                  (                                                            (                                                                        w                          LO                                                +                                                  w                          IF                                                                    )                                        ⁢                    t                                    )                                            +                              sin                ⁡                                  (                                                            (                                                                        w                          LO                                                -                                                  w                          IF                                                                    )                                        ⁢                    t                                    )                                                      ]                                              Equation        ⁢                                  ⁢        1                                                      cos            ⁡                          (                                                w                  LO                                ⁢                t                            )                                ⁢                      sin            ⁡                          (                                                w                  IF                                ⁢                t                            )                                      =                              1            2                    ⁡                      [                                          sin                ⁡                                  (                                                            (                                                                        w                          LO                                                +                                                  w                          IF                                                                    )                                        ⁢                    t                                    )                                            -                              sin                ⁡                                  (                                                            (                                                                        w                          LO                                                -                                                  w                          IF                                                                    )                                        ⁢                    t                                    )                                                      ]                                              Equation        ⁢                                  ⁢        2            
Equation 1 identifies the operation of the mixer 412, and Equation 2 identifies the operation of the mixer 414. The signals mixed by the mixers 412 and 414 are transmitted to an adder 416. The adder 416 adds the signals received from the mixers 412 and 414. The operation of the adder 412 is set forth below, using Equation 3:
                                                        1              2                        ⁡                          [                                                sin                  ⁡                                      (                                                                  (                                                                              w                            LO                                                    +                                                      w                            IF                                                                          )                                            ⁢                      t                                        )                                                  +                                  sin                  ⁡                                      (                                                                  (                                                                              w                            LO                                                    -                                                      w                            IF                                                                          )                                            ⁢                      t                                        )                                                              ]                                +                                    1              2                        ⁡                          [                                                sin                  ⁡                                      (                                                                  (                                                                              w                            LO                                                    +                                                      w                            IF                                                                          )                                            ⁢                      t                                        )                                                  -                                  sin                  ⁡                                      (                                                                  (                                                                              w                            LO                                                    -                                                      w                            IF                                                                          )                                            ⁢                      t                                        )                                                              ]                                      =                  sin          ⁡                      (                                          (                                                      w                    LO                                    +                                      w                    IF                                                  )                            ⁢              t                        )                                              Equation        ⁢                                  ⁢        3            
As shown in Equation 3, the adder 416 outputs an upper side band signal having a frequency obtained by adding the frequency of the LO signal and the frequency of the IF signal. In other words, when the SSB 308 receives a signal having a frequency of 528 MHz from the phase shifter 410 and a signal having a frequency of 264 MHz from the phase shifter 408, the SSB 308 outputs a signal having a frequency of 792 MHz.
The SSB 312 performs the same operation as the SSB 308. In other words, when the SSB 312 receives a signal having a frequency of 4224 Mhz from phase shifter 420 and a signal having a frequency of 264 MHz from a selector 418, a subtracter 430 outputs a signal having a frequency of 3960 MHz. When the SSB 312 receives a signal having a frequency of 4224 MHz from phase shifter 420 and a signal having a frequency of 264 MHz from the selector 418, an adder 432 outputs a signal having a frequency of 4488 MHz. When the SSB 312 receives a signal having a frequency of 4224 MHz from the phase shifter 420 and a signal having a frequency of 792 MHz from the selector 418, the subtracter 430 outputs a signal having a frequency of 3432 MHz, and the adder 432 outputs a signal having a frequency of 5016 MHz.
As described above, the conventional SBG includes a plurality of SSBs, a plurality of dividers, a plurality of switches, and a plurality of phase shifters. Thus, this SBG consumes a large amount of power. Also, since the SBG uses a high frequency band, several parasitic components are generated in a mixing process. Thus, an I signal cannot exactly match with a Q signal. Also, isolation performance of the switches becomes deteriorated. Moreover, harmonics components are generated by the plurality of dividers and a plurality of mixers. As a result, signals having undesired frequencies are generated.